Process of making portland cement from coal ashes



Patented Aug. 30, 1932 D. STATES VTILLIAM M/GUERTLEIt, OF'BERL'IN, ennmanmn ssien oa 170 THE ELECTRJICSMELT- ING & ALUMINUM COMPANY, or CLEVE AND, oHIo; AoonroBA'noN or 01110 rnocnss or mAxmszeonrizaiin cniurmrraom COAL AsIiEs- No Drawing.

coal ashes a substantially iron-free siliceous material suitable for cement or chemical manufacture. Q

Another object of my invention is to obtain from coal ashes which are partially fused and exist in a very finely .dividedif orm after the burning of thecoal' a siliceous materialsuit; able for the manufacture of cementand to obtain such siliceous material, by treating the coal ashes in a simpleandeificient 'in'ariner according to my process. i i

A further object of nyvinv entionistol se-j cure such siliceous material from coal ashes by the use of an acid process-Whichdueto the by-products obtained according'to my process enables me to secure material at a very low cost fromdproducts; hitherto -not used for this purpose,"Which products have heretofore been considered ivaste products,

In modern powerplants steam is generated by burning bituminous coal in boilers either by the use of mechanicalvstokers' orby tlie burning of finely powdered coal: ,II1:thlS

last system the coal is groundto, a yery finecondition and is thenrzburned by means of special burners whereby the coal is propelled into an incandescent fire box'tog'e'ther with air whereupon the carbon ofthe coal is largely burned out producing ma hot flame} The ash of the coalremains suspendedin the flue gasesand by Virtue ofits position and of the very high temperature of the flame, the ash particlesbecome morejor less vglobular in shape, fused or semi-fused and certain chemi cal and physical "transformationstake place Which are discussed later. i 1 a f The ash content of bituminous coalv varies from three percentto fifteen percent of the coal Weight and since the coal is very finely divided prior to burning it will appreciated that the ash particles formed will be much finer even than thecoal. Samples have been observed which sho vthat 991% of the ash passes through a- 100 meshscreen and 90% through a '300 mesh screem; It is very diifia naaon filed March a 21,

1630. ,Serial No. 43,941

cultto reinovesuch finely divided particles froin' the hot fiuegases; but such removalhas in" some 'inst imies been required for when the ashes have been discharged through the stacks of the power plantsthey have gradually set: tledt on the surrounding country' tolthe detrimentofvegetation, buildings and people in the neighborhood; ,Power lants such are located in or near large citiesjsornetimes sepaf rate hundreds of tons of suchfash from their stack gases each twenty four hours. methodfor such separation is by means "oi a Cottrell electrostatic dust precipitatorQ The disposal of this finely divided ash has been a serious problem and a source of ex- 7 Inthe operation ofthe Cottrell electrostatic dust precipitator for the separation of i the ash particles from the hot gas stream; the

line gases fromthe boilers are drawn'by means er a suction ian through; this device; 'vvhich consists essentially of positive and negative Pole W r by mea ta ve tarz o 1 0,0 0 to 150,000 volts an electrical} discharge passes. tlllfoughthe moving gas strealn'al fldla charge or, pote1 1ttia1 isjtherebv placed on the ash particles which "causesthem ,to be attracted. to one pole and to be'depositedfthereupon from which they falljonare scraped to a bin" underheath, I f I y Thetemperature of theflame. producedin burning powdered 'coalisu, vvard 'of2000 (1;, butthe temperature ofyt effl ie' gases falls rapidly in the boilers and {lines until in dust precipitatorlthe temperature of the gases is only about 500 ,C, Thishigh initialtem 'perature and comparatively rapid cooling ing out of the process. A I I An initial efiectof thehigh flameteniperatureisto burn out thecarbon andtod srupt thef nineral composition and-to drive out the PATENTOFFICE?) combined water and another effect is to heat the ash particles to practical fusion. Now when this fused particle is cooled in the boiler and flues, more or less rapidly as the case may be, certain crystal forms or minerals are formed. It is-possible that the composition produced is somewhat influenced bv the electrostatic discharge in the dust precipitator although this is not definitely known. At any rate theash produced as described has certain properties diflerent from the original minerals and different from most naturally.

occurring minerals. First, the iron content of the original coal forms-and separates into a magnetic oxide of iron, largely Fe O which may belargely separated from the ash by means of a magnetic separator and which then becomesa product of value in the art as a yin-int pigment or as iron ore of very high meta li'c' iron content. Second, the ash may be treated with mineral acids such as HCl, HNO H 50; or HClO- or combinations of these to dissolve the base minerals such as alumina,'any' iron'oxide that may remain after the magnetic separation, calcium or magnesium oxides, etc., leaving a residue which is essentially silica and which forms an improved raw material for cement and chem-. ical manufacture. r

If the analysis of the ashes and the economic carrying outof this process to produce a siliceous hydrate is such that it is desirable to remove and recover a considerable portion of thealumina content of the ashes, this may bereadily done as will be more fully ex-' plained hereinafter. i

It is well known that thesolubility ofalumina and the basic content of clays, and similar minerals, in mineral acids, may be increased by roastingthem within a very narrow range suitable for the particular clay in question. Such a range is usually less than C. in order to secure the most efficient extraction of the basic content of the clay. If, however, these clays are heated to atemperature of approximately 900 (1, or above, the basic content is practically insoluble, and in some cases less than 1% can be extracted by subjecting the roasted clay to the same mineral acid treatment as will extract 7 0% of the basic content if the proper roasting temperature is observed. I havefound that a high extraction of the bases may be readily obtained from the ashes from powdered coal with the use of suitable mineral acids, notwithstanding the fact that such ashes have been heated to temperatures considerably more than 900 C. The reason for this may be that the ashes are partially fused and rapidly cooled orfquenched, and thus the solubility of the basic content increased.

I have also found that the same condition obtains in powdered ashes derived from the grinding of clinkers fromthe burning of sioz 40-50% 46.9% Al' O 25-35 29. 3 Fe O FeO 9-15 11. 7 Mg() 0. 4-1. 3 .9 CaO 2. 3 2. 6 'l iO 1 1.3 Carbon 5-8 6.5 Unclassified (D) .8

The composition of the ashes produced is variable due to the fact that different coals usedas fuel vary as to their ash content and as to the composition of such ash, and also i due to the fact that the conditions under which the coal is burned is variable, the flame temperature fluctuating.

In carrying out my process a slurry of the powdered coal ash and water is formed and this slurry can be pumped and stored in tanks and treated without serious difficulty; One convenient method of removing. the magnetic iron is to pass this slurry through a magnetic separator of any'suitable design and separate the magnetic oxide of iron which can readily be disposed of as a paint pigment or as iron ore of high iron content. After removal of the magnetic iron the residue is preferably treated with a suitable quantity of mineral acid, eith'er H61, HNO H SO or HClO or combinations of these acids, to dissolve such portion of the remaining bases from the asn that may be desired. Heat generated by the dissolving reaction is usually"- sufficient to maintain the solution hot, but I can heat the solution if desired.

I have found that one good method for carrying out this process is by the use of hydrochloric acid in an aqueous solution in a strength of from 5 to 20%, depending upon the physical properties and the analysis of the particular coal ashes. It is to be understood, however, that two or more of the above acids may be used simultaneously, if desired.

.By adding more or less acid, and varying the time and temperature of treatment, I can control the extraction of alumina Within the desired economic range. By my process I extract the amount of alumina from the ashes which the economic conditions make it desirable to extract in order to recover this alumina as a valuable by-product. That is, if it is moreexpensive to make a substantially complete extraction of alumina than is co1ninercially practical for the value of the alu-.

mina recovered, then only a portion of this alumina may be extracted, leaving the remaining alumina in the siliceous hydrate for the manufacture of cement.

Under favorable conditions it may be desirable to extract all of the alumina and other basic content of the ash in order to recover the alumina, leaving substantially pure siliceous h 'drate for the manufacture of cement 'or or the manufacture of sodium silicate.

It will thus be seen that my process afiords a very simple and efiicient means for obtaining siliceous hydrate from coal ashes with the commercial advanta es of obtaining the valuable by-products of iron oxide and such alumina as may be economically extracted, and this extraction can be controlled according to the desired results to be obtained.

It will also be seen from theianalysis of coal ashes that if it be desired for economic reasons not to extract all of the alumina, the basic content left in the residue is such that the residue is desirable for cement manufacture, and a less amount of clay and lime need be added for the manufacture of Portland cement.

If, however, the desired end product be silica hydrate for the manufacture of sodium silicate then substantiall all the basic content of the ash should extracted inthe manner above set forth. In case it is desired to use this residue for the manufacture of sodium silicates, the silicahydrate can be digested with caustic soda or heated to fusion with soda ash, as is well known.

Furthermore, it is to be understood that the particular com unds disclosed, and the procedure set fort are presented for purposes of explanation and illustration and that various equivalents can be used and modifications of said procedure can be made without departing from my invention as defined in the appended claims.

What I claim is:

1. The process of producing siliceous material, mainl composed of silica hydrate, from coal as es which have been su jected to a sufliciently high temperature so that upon cooling at least some magnetic oxide of 7 iron will be formed, which consists in magnetically extracting the ma etic ironfrom the ashes and treating the as es with mineral acid to dissolve the basic content, and separating the siliceous material from the acid solution whereby a silica hydrate suitable for the manufacture of cement is produced.

2. The process of treating ashes from powdered coal which have been subjected to a sufficiently high temperature so that upon cooling at least some magnetic oxide of iron will be formed, which consists in subjecting the ashes to the action of a magnetic se arator to extract the iron oxide, treating t e i of Portland cementgwhich consists in ,mag-

ashes with a mineral acid tu dissolve :the: basic content, separating: the solution from: the residue whereby a suitable raw siliceous material for the manufacture or. cement is produced. a. i 1 1 The process of treating partially sins tered, finely dividedvashesafrom burning powdered" coal, which consists in: subjecting the ashes to the action of=a.magnetic:sep-w arator to extract 'theiron oxide, treating the ashes with a 1 solutioni of 1 hydrochloric r acid under suitable conditions 1 to; extractthe 'de-: sired "basic content, and'g separating ithe siliceous residue l with: the remaining basic content from thesolution whereby :asuitable raw material for themahufacturfi of Pei-tr. land :cementf isproduced. ,u.;

s; 4. process- 0f treatmgupartially ein:

teredfifinely divided ashes. fromburning powdered coal, which' consists intr'ea'ting the ashes-lwith a solution of hydrochloric acid under suitable conditions tog extract the de 'sirejdz; basic content, and separating the siliceous residue; with the remaining basic content from the solution whereby a suitable raw material for the manufactureof Port: land cement:is produced; 5. The process ofemanufacturingaiisiliceous material suitable for the; manufacture netically; extracting the ma netic iron con-. tent of the partially fused as es produced by the burningwofpowderied coal,.,t;reating the ashes. with an aqueous jsoluti'onqzof hydrochloric-acid todissolve all the basic content, 10

and: separating the siliceousresidue from the field s0lution.- I .H '-i ,:j;. r J 1 .6. The 'rocesssofwtreating .coal; ashes to obtain a sllicious-material mainly; comp e of silica, hydrate, which comprgise's burning the coal at a sufiicientlyhighgtemperature to parti'all fuse; the? sheaewh by' t e: bases arelmfa e more soluble, subjectinggthe ashes to1the action 0f; aj magnetic; separator-to ex tractthe magnetic iron content of the no treating the ashes with a, mineral ticidtqydissolve the basic content, and separatingthe siliceous maaaial if iom t jej jplu 7. The process of treating coal ashes to obtain a silicious material composed of silica 116 hydrate and a comparatively large percentage of the basic content of the ashes as a byproduct, which comprises burning the coal at a temperature of at least 900 C. to partially fuse the ashes and to render the basic no content of the ashes more readily soluble in mineral acids, treating the ashes with a mineral acid to dissolve the basic content, and separating the silicious material from the solution.

8. The process of treating coal ashesto obtain a silicious material and a comparatively large percentage of the basic content of the ashes asa by-product, which comprises burning powdered coal at a temperature sub- 3'0,

stantially above 900" G., ttherebyobtai ning ashes in a; substantially: fused state, cooling the ashes napidLy' and treating them with an aeidrto: dissolve the basic. content,eandfinally separating the siliceous material from J-the solutions. 1 9.11m process;-of.-treatingzcoal' ashes in which sqme' iron is-present to obtain a siliceous material, magnetic-oxide of ironuand basieimateriehiwhichcomprisesburningcoal at a:temperatureofiat:least.90(). C. to partially fuse the ashes, therebyoxidizing the iron into; armagnetic form, and effecting, a change in. the basicingredients of the ashes so as to; render-them: more soluble. in. mineral acids, subjecting-the ashesto the, action of a magnetic separator'toiremove themagnetic iron oxide,treating:the ashesito dissolvethe ba'sio content; andi separating thesiliceous material fromg the solutiom I 10. The= process of treating coalv ashesfnin which some iron isprsent to. obtain asili-' ce0us';m'aterial magnetic oxide of iron sand basic material, which comprises burning powdered ooal at a temperature substantially above 900 0;, thereby obtaining ashes in a substantially fused state, cooling the ashes rapidiy,'subjeoting-them toe magnetic separatortoremove the magnetic oxide,xtreating the ashes t dissolve the basic content, and

separating-the siliceous material from the solution.

11;. The process which some ironis present to obtain siliceousmaterial, iron oxide and basic material having a high aluminum content, which comprises burning powdered coal at a temperamre of substantiallyabove 900 Cl, thereby obtaining ashes in az'substantiall'y- -fused state, cooling the ashes rapidly, extracting the magnetic' iron ox-ide which is formed, treating thepowdered asheswith a mineral acid todissolve the basic content,- and separating theisilic'eous material from'the solutiim.

m a V WI LLIAM*ML of treatingcoal ashes'in I signw 

